Some vehicle engine systems utilizing direct in-cylinder injection of fuel include a fuel delivery system that has multiple fuel pumps for providing suitable fuel pressure to fuel injectors. This type of fuel system, Gasoline Direct Injection (GDI), is used to increase the power efficiency and range over which the fuel can be delivered to the cylinder. GDI fuel injectors may require high pressure fuel for injection to create enhanced atomization for more efficient combustion. As one example, a GDI system can utilize an electrically driven lower pressure pump (i.e., a fuel lift pump) and a mechanically driven higher pressure pump (i.e., a direct injection pump) arranged respectively in series between the fuel tank and the fuel injectors along a fuel passage. In many GDI applications the high-pressure fuel pump may be used to increase the pressure of fuel delivered to the fuel injectors. The high-pressure fuel pump may include a solenoid actuated “spill valve” (SV) or fuel volume regulator (FVR) that may be actuated to control flow of fuel into the high-pressure fuel pump. Various control strategies exist for operating the higher and lower pressure pumps to ensure efficient fuel system and engine operation.
In one approach to control the direct injection fuel pump, shown by Hiraku et al. in U.S. Pat. No. 6,725,837, a controller performs a series of calculations to control a direct injection fuel pump and direct injectors of an engine. In the related fuel system, a solenoid valve is switched on and off to inhibit or allow fuel to enter the direct injection fuel pump, thereby varying the discharge rate of the pump. To achieve the target fuel ejection volume of the pump as controlled by the solenoid valve, a correction time width is calculated based on characteristics of pump and injector operation. In an example, the controller detects running status of the engine from a variety of parameters to determine injection start timing and a target injection time width. Furthermore, the controller calculates a discharge start timing and a discharge time width of the direct injection fuel pump based on the parameters. The parameters include the acceleration opening, crank angle, and engine speed. By checking overlap between the injection period and discharge period of the pump, values are determined that are used to find the correction time width of the injectors.
However, the inventors herein have identified potential issues with the approach of U.S. Pat. No. 6,725,837. First, while the method of Hiraku et al. may provide control of the direct injection fuel pump for the fuel discharge rate range 0% to 100% as described, Hiraku et al. does not address various problems that may arise with low fuel discharge rates, such as ranging from 0% to 15%. The inventors herein have recognized that control strategies are needed that specifically address unrepeatability and unreliability that may be associated with turning the solenoid valve on and off quickly when small pumping volumes or discharge rates are desired.
Thus in one example, the above issues may be at least partially addressed by a method, comprising: during a first condition, energizing a solenoid spill valve of a direct injection fuel pump for only an angular duration based on a position of a piston of the direct injection fuel pump; and during a second condition, energizing the solenoid spill valve for or longer than a minimum angular duration, wherein the solenoid spill valve is deactivated after a top-dead-center position of the piston is reached. For example, the first condition includes when a trapping volume fraction of the direct injection fuel pump is above a threshold and the second condition includes when the trapping volume fraction is below a threshold. The trapping volume fraction, or displacement or pumped volume, is a measure of how much fuel is compressed and ejected to a fuel rail by the direct injection fuel pump. In this way, the direct injection pump is operated to ensure repeatability and reliability of the solenoid valve even for small trapping volumes.
In another example, the solenoid spill valve is turned on or energized when the fuel trapping volume is below a threshold, wherein the solenoid spill valve is energized for or longer than an angular duration independent of a position of a piston of the direct injection fuel pump. In some fuel systems, a sensor may measure angular position of a driving cam providing power to the pump piston so a controller can synchronize activation of the solenoid spill valve with the position of the driving cam and pump piston. In the disclosed method, control of the solenoid spill valve is applied in synchronism with the position of the pump piston during certain engine and fuel system operating conditions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.